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Beginner

Cisco 3750G-12S gigabit performance problem

Hi

I have some problems with Cisco 3750G-12S handling traffic above 700-800Mbps on gigabit interfaces.

When traffic peaks in that area network is sluggish and multicast TV streams stutter.
Running Version 12.2(55)SE4 on these if that might have something to do with it.

Also have some 3560G switches, and these does not seem to have the same problem.

Any ideas?

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VIP Expert

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The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

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Posting

I would be a bit surprised if the same traffic, with the same IOS versions, and same configuration, performs much differently on a 3560G vs. a 3750G, as generally they're the same platform, although the 3750G offers stacking.  However, the 3750G-12S is a "special" variant with a larger TCAM and additional SDM templates.  That model was actually designed for a distribution role, vs. and edge role.

If you've a gig interface that's handling 700-800 Mbps, and you have any kind of bursty traffic, I would expect some variation is performance.  A possible solution might be to use QoS to support a service level for some of your traffic.

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Beginner

There will be some burst

There will be some burst traffic, but on my Cacti interface graphs I can not see any bursts over 800Mbps.

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VIP Expert

Disclaimer

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages wha2tsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Often SNMP monitoring is on a 5 minute poll and you're seeing an "average", so 100% or greater utilization might be "hidden".

If not already doing so, you might also monitor queue drops.  If these are happening, interface is being pushed, from time to time, even beyond 100%.

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Beginner

Sorry for bringing this up

Sorry for bringing this up again.

Another tech mentioned that it might be a buffer problem on the 12S.
Anybody know if that might be the case?
Any thing that might solve this, adjust buffer size etc?

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VIP Expert

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Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages wha2tsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Yes, 3750's default buffer management, especially default QoS buffers settings, often leads to buffer drops.  Buffer tuning can sometimes provide dramatic improvements.

Are you seeing interface/queue drops?